Go to the style you want to add it to. Open the conversation_toolbar template in that style and delete all code there. Then copy and paste the code in the attachment into the conversation_toolbar and save.
Don't forget to change the site name for your site.

But just a quick question here -- how about if I wanted to have this show up in every post so that one could just use it to tweet a link to each individual post rather than tweet the first post of a thread? I tried tinkering around with this code but failed horribly LOL.